Electronic components or devices are extracted from wafers or substrates of semiconductor material for semiconductor assembly and packaging subsequently. The electronic components in the wafers which may not have moulding compound encapsulation protection are subjected to potential defects, such as cracks and chipping, during dicing processes wherein the electronic components are separated or singulated from the wafers. Presence of such cracks or chipping defects in a separated electronic component are likely to propagate around the electronic component. Due to stresses induced by environmental thermal cycling, the defects may eventually cause premature failure of the final semiconductor product assembled with the electronic component, thereby leading to quality issues of the final semiconductor product.
Manufacturers of semiconductor products or chips rely on automated optical inspection machines to inspect the defects on top and bottom surfaces of the separated electronic component. However, with reference to FIG. 1, if the electronic component 10 has crack defects 12 initiated on one or more of the side surfaces 14 of the electronic component but have not yet propagated to the top surface 16 or the bottom surface 18, the top and bottom surfaces 16, 18 would be absent of defects. The inspection machine inspecting only the top surface 16 and/or the bottom surface 18 would incorrectly pass the electronic component 10 as being free of defects. As such, defective electronic components 10 with defects on the side surfaces 14 but not on the top surface 16 or the bottom surface 18 cannot be screened out from non-defective electronic components 10.
One existing solution to this problem is the use of an inspection station in association with a turret-type die sorting machine to inspect defects present at four side surfaces 14 of electronic components 10. With reference to FIG. 2, there is shown such a turret-type die sorting machine 100 having a turret 102 and a plurality of pick heads 104 arranged circumferentially around the turret 102. The machine 100 includes an inspection station 106 for inspecting the electronic components 10 after the pick heads 104 pick and transfer the electronic components 10 to the inspection station 106. The inspection station 106 has four mirrors 108 that make use of inspection optics to inspect the four side surfaces 14 of each electronic component 10. Specifically, each mirror 108 is paired with a side surface 14 such that the four mirrors 108 capture images of the four side surfaces 14 to a camera inside the inspection station 106.
Typically, the electronic components 10 are fed to the machine 100 by using a feeding mechanism, such as a wafer table, a detaper feeder, a tray loader, a bowl feeder or a conveyor. The electronic components 10 are then separated and picked individually by the pick heads 104 to be transferred by the turret 102 to the inspection station 106. No matter which feeding mechanism is utilized, each electronic component 10 may have a different angular and translational positional offset with respect to the center of a pick head 104 after the electronic component 10 has been transferred to the pick head 104, due to an offset introduced during the die pick up process. To increase processing speed, the electronic components 10 are fed in bulk and they may be in various orientations when they are fed to the pick heads 104. Thus, both the positions and the orientations of these electronic components 10 will not be consistent with respect to the turret 102 when they are picked up and transferred to the inspection station 106, resulting in misalignment between the electronic components 10 and the inspection station 106.
As shown in FIG. 2, the machine 100 includes a precising station 110 to align the electronic components 10 with respect to the inspection station 106. The precising station 110 is positioned before the inspection station 106 such that an electronic component 10 held by a pick head 104 is first aligned to a position with respect to the focal distance and angle of the four mirrors 108 in the inspection station 106, so as to ensure the captured images of the side surfaces 14 are well-focused. Referring to FIG. 3A, the precising station 110 has motorized clamps 112 to mechanically align the electronic component 10 in terms of position and angular orientation with respect to the mirrors 108 in the inspection station 106 after the precising station 110. FIG. 3B illustrates the electronic component 10 with the side surfaces 14 being aligned with respect to the mirrors 108.
If the precising station 110 does not align the electronic component 10 before transferring to the inspection station 106, the side surfaces 14 will not be aligned in the correct focal distance and angle with respect to the mirrors 108, as shown in FIG. 4A. The misalignment will result in images that are out of focus and blur. On the other hand, if the precising station 110 aligns the electronic component 10 first, the side surfaces 14 can be aligned appropriately, as shown in FIG. 4B. The alignment will result in images that are focused and clear.
However, the machine 100 has a disadvantage when high optical resolution microscopic grade optics are used for detecting very small chipping and fine crack defects. This is because the depth of field of microscopic grade optics is limited to around ±15 μm for an optical resolution of approximately 2 μm. This means that the precising station 110 has to achieve a very high standard of precision when aligning the electronic component 10 in order to ensure that the side surfaces 14 can be accurately aligned in terms of position and angular orientation with respect to the mirrors 108 of the subsequent inspection station 106.
To achieve this standard of precision, the clamps 112 have a very low tolerance such that they can clamp the electronic component 10 tightly with very limited, or no clearance. However, this tight clamping of electronic components 10 is undesirable for wafers without protection from molding compound encapsulation as the bare die is prone to defects such as cracks or chipping caused by the mechanical clamping action. Another problem is that due to the low tolerance of the clamps 112, they cannot handle electronic components 10 with variations in sizes and dimensions. FIG. 5 illustrates the inspection station 106 inspecting an electronic component 10 with a different size which may be caused by cutting offsets arising from variation of dicing blade thickness. This size difference results in one of the side surfaces 14 (affected side surface 14′) being at a different distance from the corresponding mirror 108′ as compared to the distances between the other side surfaces 14 and their respective corresponding mirrors 108. As such, the focal distance between the affected side surface 14′ and the corresponding mirror 108′ is not ideal and the image of the affected side surface 14′ will be out of focus and blur. The image cannot be used to determine the presence of small chipping or fine crack defects on the affected side surface 14′.
Therefore, in order to address or alleviate at least one of the aforementioned problems and/or disadvantages, there is a need to provide a method and apparatus for aligning and inspecting electronic components, in which there is at least one improvement and/or advantage over the aforementioned prior art.